Yellow Perch Length-Fecundity and Length-Egg Size Relationships in Indiana
Waters of Lake Michigan
THOMAS E. LAUER*, STEVEN M. SHROYER1, JOHN M. KILPATRICK2, THOMAS S.
MCCOMISH, AND PAUL J. ALLEN
Aquatic Biology and Fisheries Center
Department of Biology
Ball State University
Muncie, Indiana 47306
1
Abstract. – This study was undertaken to quantify the length-fecundity and length-egg
size relationships for yellow perch Perca flavescens in the Indiana waters of Lake
Michigan. Data were pooled from gill net collections made in 1985-86 and 1999,
resulting in a wide length range of mature female yellow perch (172-332 mm TL). The
length - fecundity relationship was: log10F = -3.220 + 3.223 log10TL (r2 = 0.89), where F
= fecundity and TL = total length in mm. The mean preserved egg volume increased
with yellow perch TL and was represented by the equation: log10V = - 2.06 + 1.10
log10TL (r2 = 0.48), where V = preserved egg volume (mL), and TL = total length. These
results reveal that larger females produced both more and larger eggs than smaller
females. Therefore, intense harvest targeting large yellow perch (primarily females) in
the 1980s and 1990s may have had an effect on the quantity and quality of eggs spawned
by the population, possibly resulting in reduced recruitment.
2
Fecundity may be defined as the spawning potential of fish for a particular season
or alternatively, the number of ripening eggs in a female prior to the next spawning
period (Bagenal 1978). Although fecundity does not always equate to reproductive
success (fertility), it can provide an objective measure of reproductive effort (Moyle and
Cech 2000). Expanding this latter concept to include all mature females in a population
enumerates the potential egg deposition in a specific location, or population fecundity.
However, fecundity or reproductive effort may vary annually (Nikolskii 1969) based on
differences in food supply (Treasurer 1981), environmental conditions, including
variations in temperature and stress, density-dependent mechanisms (Sztramko and
Teleki 1977), and fish size (Tsai and Gibson 1971; Bagenal 1978). Larger fish with a
greater visceral space for egg development have larger ovaries, and thus more eggs than
smaller fish. It is also generally accepted that egg size also increases with body length
(Hislop 1988; Wright and Shoesmith 1988; Zivkov and Petrova 1993; Moyle and Cech
2000) although variation occurs among years in response to environmental conditions
(Bagenal and Braum 1978; Mitton and Lewis 1989). Fecundity values are often used to
calculate egg and fry survival, and ultimately, recruitment rates (Shoesmith 1990). Thus,
fecundity data are important to theoretical and empirical studies of early life-history
strategies (Heins and Baker 1993) and are essential for management policies directed
toward fish stocks (Sheri and Power 1969).
Yellow perch Perca flavescens in the Great Lakes have long been valued by both
sport and commercial interests, but management of the fisheries has been complicated
(Francis et al. 1996). The Lake Michigan yellow perch population has historically
exhibited wide fluctuations in abundance (Wells 1977). The population has been
3
depressed since the mid 1990s following a rapid decline from the highs of the 1980s,
(Francis et al. 1996; Shroyer and McComish 1998; Allen et al. 2003) despite a multistate
management strategy that consisted of restricting the recreational and commercial
fisheries in 1995, and eventual closing the commercial component in 1997. The decline
in Lake Michigan yellow perch abundance has been attributed to consecutive year-class
failures associated with a plethora of hypothesis including alewife interaction (Shroyer
and McComish 2000), food availability (Dettmers et al. 2003), and other biotic and
abiotic factors (Clapp and Dettmers 2004) that may impact the population at the critical
larval stage.
The relationship between fish length and fecundity for yellow perch in Lake
Michigan is difficult to establish when comparing historical studies on the subject. As an
example, fecundity varied from 60,000 to 102,000 eggs for fish ranging from 300-319
mm total length (TL) and was likely the result of small sample size (n = 4) for that length
class (Wells and Jorgenson 1983). In addition, Heyer et al. (2001) found a range of
11,000 to 36,700 eggs for fish 216-287 mm TL, but again, the number of spawning
individuals sampled was limited. Brazo et al. (1975) reported a fecundity range of
10,654 to 157,594 for females 190 mm to 354 mm TL. However, current trends in
maturing females in southern Lake Michigan have shown females maturing (> 50%) by
170 mm TL (Allen et al. 2003) suggesting an expanded range of females could be
included to create a larger and more robust data set. Furthermore, yellow perch in
Indiana waters of Lake Michigan appear to form a localized population in the extreme
southern end of the lake based on movement (Marsden et al. 1993), genetics (Miller
2003), and abundance (Francis et al. 1996), but no comprehensive fecundity data are
4
available for this stock. Therefore, the objective of this study was to model the lengthfecundity and length-egg size (expressed as volume in this study) relationships for yellow
perch collected from Indiana waters of Lake Michigan. These findings will further the
understanding of yellow perch recruitment and reproduction in Lake Michigan, as well
as, complement existing knowledge of yellow perch fecundity in the other Great Lakes
and elsewhere.
Methods
Yellow perch were collected for fecundity and egg volume analysis from southern
Lake Michigan using gill nets in May or early June 1985, 1986, and 1999 at a site
approximately 1.6 km NE of the Michigan City, Indiana, harbor. Nets were comprised of
nine panels of 15.2 m each, repeating three mesh sizes (51, 64, 76 mm stretch) and were
set overnight along both 10 m and 15 m depth contours following the methods of Shroyer
and McComish (1998). Total lengths (mm) and weights (g) of each fish were recorded.
From the 1985-86 catch, a total of 83 fish was collected, ranging in TL from 172 to 290
mm. The 1999 sampling objective was to collect data from large fish (>250 mm TL) that
were rare or absent in 1985-86 so as to expand the size range of study specimens. Thus,
an additional 32 fish were collected in 1999, ranging from 254 to 332 mm TL and used in
the analysis. Up to 12 fish were selected from each 10 mm size class that spanned the
range of ripe females collected (172 to 332 mm TL). Only four size classes (171-180,
181-190, 201-210 and 211-220) had 12 or more fish, and selection to these classes was
random.
Ovaries were removed, weighed, and placed into Gilson’s fluid as soon as
practicable following collection, but always within 2 hr, following methodology outlined
5
by Bagenal and Braum (1978). Eggs were allowed to soak for 7 to 17 months in the fluid
to facilitate the breakdown of the connective tissue present between the eggs. Prior to
initiating the enumeration and measuring procedures, any remaining connective tissue
was manually removed, and eggs were thoroughly rinsed.
Fecundity was estimated using a volumetric approach (Bagenal and Braum 1978).
Analysis began by pipetting eggs into a 15 mL centrifuge tube graduated in 0.1 mL
increments. They were allowed to settle for about 15-30 s and the centrifuge tube was
then tilted and lightly tapped several times to level the top of the column of eggs. The
top edge of the egg mass was then measured to the nearest 0.05 mL by interpolation. If
the ovary volume exceeded 15 mL, this procedure was repeated and values were summed
until the total volume of eggs in the ovary was measured. A small tube for measuring
subsamples of eggs was made by cutting the end off a disposable plastic micropipette tip
(100-1000 µL capacity), leaving some taper, but increasing the minimum diameter to
approximately 4 mm so that eggs would not jam in the bottom. The cut end was heatsealed, precisely 1 mL of distilled water was added to the tube with a Hamilton 705-N µL
syringe, and a fine mark was made to the tube at the meniscus. Three, 0.1 mL subsamples of eggs were collected from each ovary and were transferred to a glass petri dish
where they were enumerated manually with the aid of a digital counter. Means and
statistical variability of egg sub-samples could not be calculated as the sub-samples do
not meet the independence assumption. Fecundity for each female was calculated as:
F = nV0 / 0.3
where:
F = total fecundity.
V0 = total volume of eggs in mL
6
n = total volume of eggs in the three sub-samples
0.3 = total volume of the three sub-samples in mL
Mean individual preserved egg volume was also estimated for each ovary, using
the formula:
VL = 0.3/n
where:
VL = mean individual preserved egg volume in mL
n = total number of eggs in the three sub-samples combined
0.3 = total volume of the three sub-samples in mL
Simple linear regression was used to estimate the length-fecundity and the length-
egg volume relationships. We log10-transformed both TL and number of eggs because
this linearizes F = aTLb, the theoretical fecundity equation according to Bagenal (1978),
where:
F = fecundity
a = constant
TL = total length (mm)
b = exponent
A log10-log10 transformation was also used for the relationship between TL and
egg size. The relationship was modeled as log10V = a + blog10TL, where:
V = mean individual preserved egg volume (mL)
a = intercept
b = constant
TL = total length (mm)
7
A homogeneity of slopes test and an analysis of covariance (ANCOVA) were used to
compare the regression equations of the 1985-86 and 1999 samples to determine whether
the individual data sets could be combined, thus forming a single length-fecundity
relationship (Zar 1999). A similar comparison was made for the 1985-86 and 1999
length-egg size relationship. We also compared our length-fecundity relationship with
previously published reports to establish degree of similarity. We plotted the 95%
confidence limits around our regression line and compared this area with the regression
lines from other studies for overlap. Although this comparison was limited because the
original raw data for all studies was not available, it did provide some measure of
similarity and comparison.
Results
Relationships between fecundity and yellow perch total length did not differ
significantly between 1985-86 and 1999 (homogeneity of slopes test: F = 1.39, df = 114,
P = 0.24; ANCOVA homogeneity of Y intercept test: F = 2.01, df = 114, P = 0.16).
Therefore, pooled data from all years was used to establish the fecundity linear regression
model (F = 919.7, df = 114, P < 0.001, r2 = 0.89, Figure 1):
log10F = -3.220 + 3.223 log10TL
where:
F = fecundity
TL = total length (mm)
Fecundity predicted by the linear regression model over the observed length range was
from 9663 eggs for a 172 mm fish to 80,469 eggs for a 332 mm fish.
8
The egg volume – total length relationship was also not significantly different
between 1985-86 and 1999 (homogeneity of slopes test: F = 0.53, df = 114, P = 0.82;
homogeneity of Y intercept test: F = 1.64, df = 114, P = 0.21). Thus, the data from both
periods were pooled and were used to form a single linear regression). We found a
positive linear relationship model (F = 106, df = 114, P < 0.001, r2 = 0.48, Figure 2)
between fish length and preserved egg volume described by the equation:
log10V = -2.06 + 1.10 log 10TL
where:
V = preserved egg volume (mL)
TL = total length (mm)
Mean egg size predicted from this linear regression model ranged from 2.58 X 10-6 mL
for a 172 mm fish to 5.36 X 10-6 mL for a 332 mm fish.
Egg production in our study was similar to the Lake Michigan study near
Saugatuck (Wells and Jorgenson 1983) as the regression lines for the studies overlapped
(Figure 3). The Brazo et al. (1975) findings near Ludington were not similar to our study
as the regression line did not fall within the 95% confidence limits detailed by our
statistics for fish in the same size ranges. However, if Brazo et al. (1975) had extended
the lower range of their study to include fish less than 190 mm, their regression line
would have likely crossed the 95% confidence interval. Furthermore, yellow perch
studies outside Lake Michigan were not within the 95% confidence limits. Formal
statistical comparisons could not be made contrasting our data with others because not all
original data sets were available, and these findings should be viewed as only suggestive.
9
Discussion
Mean fecundity for a given length yellow perch in our study was higher when
compared to fish from Chesapeake Bay, and Keowee Reservoir, South Carolina (Muncy
1962; Clugston et al. 1978), and lower when compared to Lake Ontario and Lake Erie
(Sheri and Power 1969; Sztramko and Teleki 1977) (Figure 3). Although fecundity in
some parts of southern Lake Michigan was similar to our study (Wells and Jorgenson
1983), Heyer et al. (2001) found lower fecundity for Lake Michigan fish collected off
Milwaukee although his size range of fish (216 to 287 mm TL) and number (n = 10) of
females evaluated were limited. Declines in egg production have been demonstrated for
yellow perch populations that are suffering from poor conditions, particularly deficient
food supply and limited growth the previous summer (Newsome and Leduc 1975).
Similarly, fecundity in several percid populations can be affected by growth rates and
food supply (Baccante and Reid 1988; Diana and Salz 1990; Hayes and Taylor 1994,) as
gonad production is energy intensive (Craig 1987). Parasitic infection can also influence
yellow perch fecundity (Johnson and Dick 2001), a factor that is not always considered
when evaluating gonadal productivity. Zivkov and Petrova (1993) indicated fecundity of
pikeperch Sander lucioperca in different bodies of water is determined by differences in
maturation period, lengths of life cycle, and types of female age structure. Because fish
in the southern portion of Lake Michigan may represent a single population (Marsden et
al. 1993; Francis et al. 1996; Miller 2003), it is plausible they would exhibit fecundity
traits similar to each other. Several factors could be influencing the fecundity – length
relationship for yellow perch that exists among divergent bodies of water; however
10
geographical proximity does not appear to be a principal contributing factor in southern
Lake Michigan.
Our positive egg size – total length relationship was supported by Heyer et al.
(2001), who also showed increased energy reserves (yolk) available to offspring of larger
females, as measured by dry weight and total DNA content. Egg size from the ovaries of
yellow perch just prior to spawning have been found to have a mean diameter from 0.94
mm to 1.62 mm over a fish length range from 170-320 mm TL (Treasurer 1981). In the
closely related European perch Perca fluviatilis, egg size has been found to increase with
total length and may be a compensating mechanism for populations that are highly
variable or experiencing fluctuating mortality (Volodin 1979). Larvae from larger
females (producing larger eggs) therefore may better resist starvation, feed on larger food
items, swim faster to avoid predation, disperse farther, and are subject to lower overall
mortality (Braum 1978; Wright and Shoesmith 1988; Duarte and Alcaraz 1989, Moodie
et al. 1989).
Changes in egg size and number based on fish length could affect recruitment in
fish stocks, especially in exploited fisheries where larger fish tend to be harvested,
leaving smaller fish as the main component of reproductive potential (Coates 1988). This
has important implications for the yellow perch population in southern Lake Michigan
where intense exploitation during the mid 1980s through 1997 truncated the adult size
distribution, prior to and during a decline in recruitment (Allen et al. 2003; Marsden and
Robillard 2004). The selective removal of larger yellow perch, resulting in a
predominance of smaller females in the population, would have led to fewer and smaller
egg production based on our findings. This may not be a problem during years when
11
large numbers of eggs are laid, as the quantity and quality of larvae produced may not be
limiting. However, Marsden and Robillared (2004) suggested that the suppressed female
broodstock in the Illinois wasters of Lake Michigan contributed to the decline in yellow
perch abundance in 1994 through 1997. Thus, the remaining mature females, if less in
total length, would have produced fewer eggs and eggs of lower quality resulting in
larvae more susceptible to the factors affecting yellow perch recruitment (Clapp and
Dettmers 2004). Furthermore, Marsden and Robillard (2004) concluded that the most
judicious management decision to conserve yellow perch in southern Lake Michigan was
to curtail or abandon harvest in an effort to protect the broodstock and increase spawning
potential. Had excessive exploitation not truncated the length frequencies of spawning
size yellow perch in southern Lake Michigan during the mid 1980’s to the mid 1990’s
(Allen et al. 2003; Marsden and Robillard 2004), the recent reduction in recruitment
might not have been as acute or as enduring.
Acknowledgements
This research was supported by Federal Aid in Sportfish Restoration funds
through the Fisheries Section, Division of Fish and Wildlife, Indiana Department of
Natural Resources. Ball State University provided matching funding, equipment, and
facilities. Indiana Department of Natural Resources staff collected the yellow perch in
1985-86. Dr. Carolyn Vann suggested the use of modified micropipette tips to measure
egg sub-samples. Special thanks go to Ball State University students Tom Lane, Marla
Banther, Charles Raines, Carlos Guindon, and Zachary J. Willenberg for assistance with
field or laboratory work. In addition, we extend our appreciation to Dr. David LeBlanc
and Dr. Mark Pyron for statistical assistance, review, and comments on data analysis.
12
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Footnotes (from title page):
* Corresponding author: tlauer@bsu.edu
1
Present address: Minnesota Department of Natural Resources, P. O. Box 86, Waterville,
Minnesota 56096, USA
2
Present address: Nebraska Game and Parks Commission. 301 East State Farm Road
North Platte, NE 69101, USA
19
Figure 1. Relationship between total length and fecundity of yellow perch in Indiana
waters of Lake Michigan based on the collection from two time periods.
Figure 2. Relationship between total length and preserved egg volume of yellow perch in
Indiana waters of Lake Michigan based on collection from two time periods.
Figure 3. Length – fecundity relationship for yellow perch in the Indiana waters of Lake
Michigan (this study - solid line along with 95% confidence intervals). Six other studies
are shown for comparison, with regression lines plotted from published slope and
intercept values. All regression equations were transformed using log10 – log10
transformations except (a), where length was not transformed. In addition, the length
range of each regression line approximated (within 5 mm) the data range used to generate
the equation.
20